Amine functional silicones are of wide utility as releasing agents, surfactants, copolymers in urethane or epoxy composites, polycarbonates and polyamides. They also find utility in corrosion resistant coatings and polishes. Present commercial methods for manufacture of these materials suffer from several disadvantages.
One current commercial method involves preparation of aminopropyl terminated siloxanes, by reaction of a cyclic siloxane such as octamethylcyclotetrasiloxane with an end-capper such as bis(aminopropyltetramethylsiloxane) and a basic catalyst such as potassium hydroxide, carried out at 80-100.degree. C. Disadvantages of this process include: first, the endcappers are not always readily available and require synthesis by reduction of cyano compounds by high pressure hydrogenations or pyrophoric metal hydrides. Second, the residual endcapper is high boiling and not readily removed from the polymer by simple distillation techniques. Third, the basic catalyst must be removed by extraction or thermal degradation to prevent side reactions in future processes.
For preparation of internally functionalized aminopropyl siloxane homopolymers or copolymers, a second process is used involving reaction of a cyclic siloxane such as octamethylcyclotetrasiloxane with an endcapper such as hexamethyldisiloxane, and a cyclic aminopropyl functional siloxane is carried out, with a basic catalyst at 80-100.degree. C. This process has a number of disadvantages or shortcomings, which include the following. Disadvantages of this process include: first, the cyclic aminopropyl functional siloxanes are not commercially available and require synthesis by hydrolysis of aminopropyl dialkoxysilanes. Second, the residual cyclic aminopropyl functional siloxanes are high boiling and not readily removed from the polymer by simple distillation techniques. Third, the basic catalyst must be removed by extraction or thermal degradation to prevent side reactions in future processes.
We have discovered a new method for preparation of aminopropyl or aminoalkyl functional siloxanes that overcomes these disadvantages and shortcomings of previous methods.
Several disclosures made in United States Patents will now be discussed, illustrating the state of the art of siloxane chemistry.
U.S. Pat. No. 3,715,334 to Karstedt disclosed platinum-vinylsiloxane catalysts for hydrosilation reactions, where the catalysts were substantially free of chemically combined halogen. This disclosure did not teach or suggest the use of these catalysts for making aminofunctional compositions.
U.S. Pat. No. 3,775,452 to Karstedt disclosed platinum containing siloxane catalysts for hydrosilation reactions, and a method for making such catalysts. This Patent did not teach or suggest the use of these catalysts for making aminofunctional compositions.
U.S. Pat. No. 3,890,269 to Martin disclosed a method for preparing aminofunctional organopolysiloxanes, where the method comprised equilibrating an organopolysiloxane and an aminofuntional silane or siloxane in the presence of a catalyst. The catalysts that could beused in the method were disclosed as being bases such as alkali metal hydrides, e.g., sodium hydroxide, potassium hydride, lithium hydride, cerium hydride; alkali metal alkyls, e.g., ethyllithium, ethylsodium, butyllithium; alkali metal alkenyls, e.g., vinyllithium; alkali metal ayls, e.g., biphenylsodium, phenyllithium, potassium naphthalene, and lithium naphthalene. Alkali metal alkyls were preferred for use in the method. Platinum containing catalysts were neither taught, nor suggested for use in the method of U.S. Pat. No. 3,890,269.
U.S. Pat. No. 5,446,113 to Lewis disclosed a method for preparing heat curable organopolysilxane compositions by reacting a silicon hydride siloxane with a devolatilized mixture of a vinyl silicone fluid and a reaction product of a zero valent platinum complex and a vinylsilane. The use of this disclosed method for preparing aminofunctional siloxanes was neither taught, nor suggested in U.S. Pat. No. 5,446,113.
A need exists therefore for a method for preparing aminofunctional siloxanes that avoids the disadvantages and shortcomings of the methods described above. A need also exists for a one pot method of making aminofunctional siloxanes, the method being easy and rapid to conduct. Still another need exists for a one pot method of making aminofunctional siloxanes using a neutral catalyst, thereby avoiding interference with further reactions of the amino group.
To overcome the shortcomings of known methods above, and to satisfy the outstanding needs outlined above we have now discovered a new method for preparing aminofunctional siloxanes.